The effect of voltage, temperature and morphology on electrical treeing in polyethylene blends

254

109

The amount of literature on partial discharge (PD) and partial discharge induced degradation is vast. In the past 10 -20 years significant progress has been made on research within partial discharge induced aging of dielectrics. Researchers now agree on the main mechanisms pertaining to this topic. With the advent of a new generation of dielectrics of which many properties now can be affected by the introduction of small amounts of nano-sized particles it seems to be a good moment to review the progress on the understanding of PD induced aging. Focusing on internal partial discharge in solid polymeric insulation this paper tries to identify achievements and at the same time challenges still to be solved.

Section: The Effect Of Temperaturementioning

confidence: 99%

Degradation of solid dielectrics due to internal partial discharge: some thoughts on progress made and where to go now

Morshuis

2005

254

109

“…Research conducted into electrical treeing has also concluded that insulation endurance is reduced at higher temperatures [10,11]. Kim et al [12] suggested that exposure to the oxidizing effects of partial discharge created a silica-like layer on the uppermost surface that can become porous and cracked.…”

Section: Effects Of Temperaturementioning

confidence: 99%

The effects of pressure and temperature on partial discharge degradation of silicone conformai coatings

Emersic

Lowndes

Cotton

et al. 2017

The partial discharge damage rates for silicone-coated printed circuit boards have been quantified in a series of experiments at pressures and temperatures relevant to the aerospace industry (down to 116 mbar, -55°C to +70°C) and up to 6 kV. Surface cracking was observed, and damage magnitude was found to be non-linear with coating thickness, with thinner coatings experiencing relatively greater damage rates. This is attributed to higher surface electric fields for a given energisation voltage. Increasing temperature or reducing pressure increased the rate of damage. For coating thicknesses less than 100 µm, reducing pressure to 116 mbar (1 mbar = 100 Pa) increased the relative crack growth rate by nearly an order of magnitude. Temperature change had the most profound influence on damage; low temperatures were observed to substantially reduce damage rate, with very little or no damage observed, whereas higher temperatures substantially increased damage rate, with the resulting magnitude of surface damage too large to quantify. Silicone coatings of thickness greater than 250 µm showed no appreciable damage from partial discharge when aged at either low pressure or high temperature at voltages up to 6 kV. Corresponding damage-free surface electric fields are computed. No samples were observed to fail, indicating the robustness of high quality silicone coatings. Possible causes of crack formation in silicone are discussed.

“…Using the real size of electrical trees in experiments (as shown in Figure 3c) and presuming that the radius of uniform distributed space charge screening shell is r 1 = 0.5 mm and the distance between the tips of electrical trees and ground electrode is r 2 = 2.5 mm (assume the length of electrical tree is 0.5 mm), and the applied voltage is U = 7 kV, then the real electrical field can be estimated as follows: [2] ), so the space charge screening shell indeed inhibits the growth of electrical trees. From the polarization photos and SEM (Scanning Electron Microscop), it is evident that the big spherulites exist among vine-branch-like trees ( Figure 11) and there is a large morphology difference (Figure 12) between the inner and outside layer of the sample clearly.…”

Section: The Electrical Trees At Low Frequency and The Non-uniform Crmentioning

confidence: 99%

“…The necessary condition for the extension of tubular cracks is that the sum of both the electrostatic energy W es and the electric mechanical energy W em stored in tree channels must be larger than the sum of both the plastic deformation energy W fp and the surface energy W fs , their values can be approximately given by the following equations [16] (2) where is the surface tension, is a correction factor, y is the yield stress, and L and r are the length and radius of the cylindrical cavity of the electrical trees, respectively.…”

Section: The Electrical Trees With Residual Stress At Low Frequencymentioning

confidence: 99%

“…The electrical trees can be initiated from various defects in cable insulation, such as impurity or local high electric field due to the protuberance of semi-conducting shielded layer. It is found that the factors responsible for initiating and propagating of electrical trees in polyolefin cable insulation depend upon not only the cable manufacturing technique, 12 October 2009. the frequency of applying voltage, but also the impurity content, the internal residual stress and physical morphology of insulation material [1][2][3][4][5][6][7][8]. With the increasing applications of 220 kV and above, the insulation of XLPE cables becomes thicker and the harmonic problems in power system could not be neglected in recent years.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Investigations of electrical trees in the inner layer of XLPE cable insulation using computer-aided image recording monitoring

Xie

Zheng

2010

Using a computer-aided image recording monitoring system, extensive measurements have been performed in the inner layer of 66 kV cross-linked polyethylene (XLPE) cables. It has been found that there are three kinds of electrical trees in the samples, the branch-like tree, the bush-like tree and the mixed tree that is a mixture of the above two kinds. When the applied voltage frequency is less than or equal to 250 Hz, only the mixed tree appears in XLPE samples, when the frequency is greater than or equal to 500 Hz, only the dense branch-like tree develops, both of which are attributed to the coexistence of non-uniform crystallization and internal residual stress in semicrystalline XLPE cables during the process of manufacturing. Through the fractal analyses of these electrical trees, it has been found that both the propagation and structure characteristics can be described by fractal dimension directly or indirectly. It is suggested that the propagation and structural characteristics of electrical trees are closely related to the morphology and the residual stress in material at low frequency, i.e., the propagation characteristics of electrical trees depends upon not only the boundaries between big spherulites and amorphous region, but also the impurity, micropore concentration and the relative position of needle electrode tip with respect to spherulites or amorphous region in the low frequency range. However, at high frequency, it has nothing to do with the morphology of material. It is suggested that the injection and extraction process of charge from and to dielectrics via the needle electrode are more intense at high frequency than in low frequency. Thus, it can form relatively uniform dielectric weak region in front of needle electrode, which leads to similar initiation and propagation characteristics of electrical trees at high frequency.